Rotating shaft coupling assembly

ABSTRACT

A rotating shaft coupling assembly includes a first rotating shaft defining a step at a longitudinal end. A second rotating shaft has a longitudinal end to be received against the step of the first rotating shaft such that the first and second rotating shafts form an overlapping portion. A coupler sleeve including a shape memory alloy is disposed about at least the overlapping portion of the first and second rotating shafts to couple the shafts together.

FIELD OF THE INVENTION

This invention relates generally to a rotating shaft coupling assembly,and more particularly to a rotating shaft coupling assembly including ashape memory alloy.

BACKGROUND OF THE INVENTION

The traditional method for rigidly coupling two shafts is to use aspline that is piloted on both ends or a threaded connection that hastwo piloting surfaces. The purpose of the piloting features (generallyeither two diameters or a diameter plus a shoulder) is to ensure thatthe coupling maintains concentricity and colinearity of the two shaftaxes. This technique for shaft coupling requires that the mating shaftends are designed and machined specifically for the coupling function.

In the situation where a rigid coupling is to be made to a shaft endthat is not specifically designed for the coupling, there are severalmethods available. The most popular include:

-   -   1) Simple press fit;    -   2) Press fit with a clamping collar; or    -   3) Tapered compression coupling such as Ringfeder Corp. Locking        Elements™ or Fenner Mannheim Trantorque® coupling.

For high-speed applications the coupling must be able to maintain areasonable balance of the assembly, which tends to exclude the clampingcollar devices. Aerospace requirements favor small size, highreliability and robust design. The Trantorque® couplings are robust butnot small; whereas the simple press fit is small but not robust.

Accordingly, it is an object of the present invention to provide arotating shaft coupling that overcomes the above-mentioned drawbacks anddisadvantages.

SUMMARY OF THE INVENTION

In an aspect of the present invention, a rotating shaft couplingassembly includes a first rotating shaft defining a step at alongitudinal end. A second rotating shaft has a longitudinal end to bereceived against the step of the first rotating shaft such that thefirst and second rotating shafts form an overlapping portion. A couplersleeve fabricated from a shape memory alloy is disposed about at leastthe overlapping portion of the first and second rotating shafts tocouple the shafts together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional, side elevation view of a rotating shaftcoupling assembly in accordance with a first embodiment of the presentinvention.

FIG. 2 is a cross-sectional, side elevation view of a rotating shaftcoupling assembly in accordance with a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a rotating shaft coupling assembly inaccordance with a first embodiment of the present invention is indicatedgenerally by the reference number 10. The assembly can be used in, forexample, gas turbine engines, but is not limited in this regard. Theassembly 10 includes a first rotating shaft 12 and a second rotatingshaft 14 to be coupled together. In gas turbine engine applications, thefirst rotating shaft 12 can be, for example, an integratedstarter/generator (ISG) shaft fabricated from a durable alloy such asIncoloy A-286 (an age hardenable iron-nickel-chromium alloy) or Inconel718 (a flowformed nickel-base superalloy). The second rotating shaft 14can be, for example, a high pressure compressor (HPC) tie boltfabricated from a durable alloy such as Incoloy 909 (anickel-cobalt-iron alloy).

As shown in FIG. 1, the first rotating shaft 12 defines a shoulder orstep 16 so as to form a first step surface 18 on one side of the step 16and a second step surface 20 on the other side of the step. Alongitudinal end 22 of the second rotating shaft 14 is abutted againstthe second step surface 20 and the shoulder or step 16 such that anouter surface 24 of the second rotating shaft adjacent to the step isgenerally flush with the first step surface 18 of the first rotatingshaft 12 adjacent to the step. For a traditional press fit connection,the first rotating shaft 12 and the second rotating shaft 14 would becoupled via a radial interference fit at the second step surface 20. Thepresent invention has a radial clearance at the second step surface 20,such that the rotating shafts 12, 14 can readily be assembled andsubsequently positioned.

A coupler sleeve 26 fabricated from a shape memory alloy (SMA) isdisposed about at least portions of the first and second rotating shafts12, 14 which overlap one another adjacent to the shoulder or step 16. Asinstalled, the coupler sleeve 26 has been expanded by plasticdeformation while in the weak phase (martensite, for Tinel alloys), andhas been stored below the transformation temperature until installationin the coupling. When the coupler sleeve 26 has been properly positionedduring installation, it is heated to a temperature greater than thetransformation temperature causing the SMA material to transform to thestrong phase (austenite, for Tinel alloys). This transformation causesthe coupler sleeve 26 to return to its original dimensions ifunrestrained, that being of a smaller diameter than the outer diameterof the first rotating shaft 12 and the second rotating shaft 14. Theresulting dimension of the coupler sleeve 26 results in a radialinterference fit between the coupler sleeve and the rotating shafts 12,14, and also a radial interference fit between the first rotating shaft12 and the second rotating shaft 14 at the second step surface 20. It isthe interference fit at the second step surface 20 that determines thealignment of the rotating shafts 12, 14, and determines the friction totransmit torque from one shaft to the other. The coupler sleeve 26 beingan SMA material can be similar to a Cryofit® coupling including a TinelAlloy per MEPS-6151 available from Aerofit Products, Inc.

The present invention embodied in FIG. 1 presents an alternative tocreating a rigid coupling to an existing shaft that is both small,robust and maintains a reasonable balance. The fundamental basis for thecoupling as shown in FIG. 1 uses the principle of press fit, butincorporates the coupler sleeve fabricated from a shape memory alloy tobe able to generate the interference fit, and hence a significantly morerobust coupling that is relatively easy to assemble. As shown in FIG. 1,the piloting is controlled by a diameter and a shoulder, and the axialretention and torque transmission are maintained via friction and anover the shoulder feature similar to the lip on a coffee can lid orTupperware® container.

With reference to FIG. 2, a rotating shaft coupling assembly inaccordance with a second embodiment of the present invention isindicated generally by the reference number 100. The assembly 100includes a first rotating shaft 102 and a second rotating shaft 104 tobe coupled together. In gas turbine engine applications, the firstrotating shaft 102 can be, for example, an ISG shaft fabricated from adurable alloy such as a Greek Ascoloy (a chromium-nickel-tungstenmartensitic alloy) or Inconel 718. The second rotating shaft 104 can be,for example, an HPC tie bolt fabricated from a durable alloy such asIncoloy 909.

As shown in FIG. 2, the first rotating shaft 102 defines a shoulder orstep 106 so as to form a first step surface 108 on one side of the stepand a second step surface 110 on the other side of the step. Alongitudinal end 112 of the second rotating shaft 104 is abutted againstthe second step surface 110 and the shoulder or step 106 such that anouter surface 114 of the second rotating shaft adjacent to the step isgenerally flush with the first step surface 108 of the first rotatingshaft 102 adjacent to the step. At the assembly of the first rotatingshaft 102 and the second rotating shaft 104, there is a radial clearancebetween the shafts at the second step surface 110.

The first rotating shaft 102 defines a first hole 116 extendingtherethrough, and the second rotating shaft 104 defines a second hole118 extending therethrough. As shown in FIG. 2, when the shoulder 106 ofthe first rotating shaft 102 is abutted against the longitudinal end 112of the second rotating shaft 104, the first hole 116 and the second hole118 axially coincide with one another. A connector 120 such as, forexample, a pin is received through the first and second holes 116, 118to thereby secure the first and second rotating shafts 102, 104 to oneanother. Preferably, the holes 116, 118 are formed by a single drillingoperation once the first and second rotating shafts 102, 104 arepositioned together as described above. It is most effective to use aminimum of three pins 120 so that a bending moment along the axis of therotating shafts 102, 104 can be transmitted, and the shafts will behaverigidly as a single shaft.

A coupler sleeve 122 fabricated from a shape memory alloy (SMA) isdisposed about at least portions of the first and second rotating shafts102, 104 which overlap one another adjacent to the shoulder or step 106and is activated as described above to cause the radial clearance at thesecond step surface 110 to become an interference between the rotatingshafts. The coupler sleeve 122 is also used to retain the pins 120against centrifugal body forces caused by the rotation of the rotatingshafts 102, 104. The coupler sleeve 122 fabricated from an SMA materialcan be similar to a Cryofit® coupling including a Tinel Alloy perMEPS-6151 available from Aerofit Products, Inc.

The present invention embodied in FIG. 2 is a more robust embellishmentof the coupling concept shown and described with respect to FIG. 1,wherein the press fit joint is inverted, and the torque and axialretention are maintained by shouldered pins that are inserted into holesmachined after the shafts are assembled. In the embodiment shown in FIG.2, the coupler sleeve 122 maintains the radial fit at the second stepsurface 110 and captures the pins 120.

In sum, the present invention creates structure to couple shafts in arobust and compact manner—specifically where there are no couplingfeatures on an existing shaft. The present invention was conceived tocouple a shaft extension to an existing shaft for the specific purposeunrelated to the coupling itself. However the present invention can alsobe applied to repair damaged features, or to avoid the precise machiningassociated with traditional shaft coupling techniques.

As will be recognized by those of ordinary skill in the pertinent art,numerous modifications and substitutions can be made to theabove-described embodiment of the present invention without departingfrom the scope of the invention. Accordingly, the preceding portion ofthis specification is to be taken in an illustrative, as opposed to alimiting sense.

1. A rotating shaft coupling assembly comprising: a first rotating shaftdefining a step at a longitudinal end; a second rotating shaft having alongitudinal end to be received against the step of the first rotatingshaft such that the first and second rotating shafts form an overlappingportion; and a coupler sleeve fabricated from a shape memory alloydisposed about at least the overlapping portion of the first and secondrotating shafts to couple the shafts together.
 2. A rotating shaftcoupling assembly as defined in claim 1, wherein the first rotatingshaft defines a first hole therethrough, and the second rotating shaftdefines a second hole therethrough such that the holes are axiallyaligned with one another for receiving a connector pin through theholes.
 3. A rotating shaft coupling assembly as defined in claim 1,wherein the first rotating shaft is an integrated starter/generatorshaft, and the second rotating shaft is a high pressure compressorshaft.
 4. A rotating shaft coupling assembly as defined in claim 1,wherein the coupler sleeve is made from a nickel titanium shape memoryalloy.
 5. A rotating shaft coupling assembly as defined in claim 1,wherein the coupler sleeve is made from a Tinel shape memory alloy.
 6. Arotating shaft coupling assembly as defined in claim 2, wherein thecoupler sleeve is configured to retain the connector pin, and to ensurethat a radial fit between the first and second rotating shafts ismaintained.
 7. A rotating shaft coupling assembly as defined in claim 1,wherein the coupler sleeve defines at least one circumferential rib foraxial location and retention of the coupler sleeve relative to the firstand second rotating shafts.
 8. A rotating shaft coupling assembly asdefined in claim 3, wherein the coupler sleeve defines at least onecircumferential rib for axial location and retention of the couplersleeve relative to the first and second rotating shafts.